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Old 10th October 2007, 10:01 AM   #1
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Default tube current

how do i know what current each tube needs?

do i just use the idle current figure..
e.g/ the current where the loadline intersects with the grid voltage line i have biased for..

cheers
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Old 10th October 2007, 10:12 AM   #2
jnb is offline jnb  Australia
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Yes, and the current will vary around this as shown up and down the loadline.

Could you perhaps give more info as to your purpose?
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Old 10th October 2007, 10:43 AM   #3
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right then i am trying to design a kt88 based single ended stereo amplifier.
i think i want to run 2 kt88s with an HT of around 450-500v through a 3.5k load (the primary winding of my output tx).

i shall be inputing about 45v pk-pk in to the kt88 is will bias for about -35v, on the load line 35v intersects at about 70mA, but ca potentialy swing from about 10-110 mA.

do i do my calculations for the power supply with the 70mA figure.

the driver stage will be a 6sn7 with an HT of about 250V and an anode load of about 27K.
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Old 10th October 2007, 04:16 PM   #4
kevinkr is offline kevinkr  United States
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Since it is a class A amplifier the 70mA idle current per channel is valid for designing your power supply, but don't fall into the trap of under specifying a power transformer for a stereo amplifier. Generally you need to take into account the non sinusoidal charging currents that flow in the rectifier circuit to charge the first cap in your power supply, unless of course you are using choke input. Typically I use a 250mA rated power transformer for dc load currents of >150mA, but no more than 200mA. Using choke input you can (marginally in some cases) get away with a 200mA transformer, however the secondary voltage will need to be substantially higher to get the same output voltage.

I recommend you download and install PSUDII from Duncan Amps and model your proposed power supply topology.

I also recommend the purchase of Building Valve Amplifiers, and Valve Amplifiers 3rd Edition by Morgan Jones. Very useful stuff here.
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Old 10th October 2007, 06:26 PM   #5
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cheers

ive got psud and valve amplifiers 3rd ed,

is it worth buying "building valve amplifiers" as well?
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Old 10th October 2007, 08:18 PM   #6
kevinkr is offline kevinkr  United States
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Quote:
Originally posted by soundbadger

<snip>
is it worth buying "building valve amplifiers" as well?
Definitely...

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